This invention relates to suspension and propulsion systems for use in transportation and, more specifically, to a single integrated device including means for suspending a vehicle from a passive roadway and an electric motor for propelling the vehicle along the passive roadway.
Efforts have long been made to develop faster, safer, and more efficient forms of transportation. The problems encountered have been numerous. This is particularly true in large cities, where traffic congestion, system costs, and pollution have become acute. The present invention addresses these problems, providing a solution to a number of them.
Two elements common to surface transportation systems are a means of suspending a vehicle with respect to a roadway and a means of propelling the vehicle along that roadway. The earliest and most common suspension systems are primarily mechanical, including wheels affixed to axles. Such systems, however, are subject to a number of shortcomings. For example, contact between the wheels and the roadway introduces significant frictional forces, which produce drag on the vehicle and reduce system efficiency. Similarly, the wear introduced by moving parts typically requires additional maintenance of the system, thereby increasing the system's cost of operation. The ride comfort and noise of the system are also deleteriously affected by the moving wheels in contact with the roadway.
One proposal for overcoming these drawbacks is the use of magnetic forces to suspend the vehicle in a noncontacting, controlled relationship to the roadway. For example, magnetic repulsion between magnet members located on both the roadway and the vehicle can be used for supsension. Similarly, the attractive force between magnets of opposite polarity, or magnets and a magnetically permeable material, such as iron, can be used to eliminate contact between the vehicle and the roadway.
Because magnetic attraction systems are inherently unstable and require closed-loop control for proper operation, electromagnets are frequently employed. The electromagnets perform vehicle suspension by adjusting the magnetic field needed to produce the desired spacing between the vehicle and roadway. Electromagnets used in suspension systems, however, are subject to a number of shortcomings. For example, electromagnets used as the primary source of suspension consume a substantial amount of energy. With electromagnets employed onboard the vehicle for this purpose, large power supplies must also be included, increasing vehicle weight and impairing system efficiency. While offboard power supplies would decrease vehicle weight, realtime control of the suspension gap between the vehicle and roadway becomes impractical. The use of offboard electromagnets for suspension would also make real-time control impractical, as well as involve large expenditures of initial captial to provide the requisite number of electromagnets.
Because of the weight, size, and power requirements of suitable electromagnets, some efforts have been made to utilize permanent magnets that contain rare-earth elements and exhibit both high magnet flux density and a relative permeability that is near unit. For example, U.S. Pat. No. 3,783,794 discloses a suspension system employing separate electromagnet and rare-earth permanent magnet elements, with the rare-earth permanent magnet element providing most of the suspending force and the electromagnet element controlling the gap between the vehicle and the roadway.
Electromagnetic propulsion systems have also been developed. For example, linear electric motors have been designed for vehicles equipped with an electromagnetic suspension system, the suspension system being either incorporated in the motor or separate. Most of the prior art effort has been directed to linear induction motors, because induction motors of a given power rating are generally lighter than synchronous motors of equal power rating. The power factor of a linear induction motor, however, is relatively low, requiring a large and heavy variable-voltage, variable-frequency power supply. In addition, linear induction motors consume a relatively large amount of energy.
While linear synchronous motors offer certain advantages over linear induction motors, prior art linear synchronous motors are also unsatisfactory in many respects. For example, while long-stator linear synchronous motors, having coil windings distributed the length of the roadway, provide a high power factor, they still consume a relatively large amount of energy and require substantial electrical conditioning for proper operation. In addition, the polyphase coil windings required for the roadway involve enormous expenditures of initial captial. Short-stator linear synchronous motors, having their propulsion coil windings located onboard the vehicle, experience the problems of real-time control and expense previously described in connection with suspension systems when offboard suspension is employed, Short-stator linear synchronous motors employing onboard electromagnetic suspension in conjunction with the onboard synchronous motor (often referred to as linear synchronous homopolar, or unipolar, motors) experience problems of substantial energy consumption and electrical conditioning requirements. In addition, prior to this invention, researchers had not been successful in constructing a uinpolar motor that incorporates permanent magnets for providing a majority of the vehicle suspension force.